Alternating current generators are well-known in the art and are used to produce alternating current output voltages of either single phase or three phase. A typical three phase AC generator of the rotating field type has field coils excited by an exciter coil on the same shaft. The exciter field excites the exciter armature, the output of which is rectified and used to excite the generator field which when rotated induces an AC voltage in the generator stator.
The DC voltage applied to the exciter field controls the exciter field strength which in turn controls the exciter armature voltage and, hence, the main field magnetic strength. As the main field magnetic strength is controlled, so is the generator output voltage induced in the generator stator.
Also well-known in the art are voltage regulator circuits which are connected to the output voltage leads from the generator stator and which control the voltage applied to the exciter field to control the strength of the main field to adjust the output voltage. Many different techniques are used to sample or sense the output voltage, one of which the inventors are familiar with includes detecting the peak of every other half cycle of the output voltage, comparing it with a desired reference value, and then adjusting the exciter field voltage up or down as required to correct the generator output voltage.
Another problem associated with utilizing voltage regulators which detect generator output and compare generator output voltage with a reference voltage is that a way must be found to bypass this regulator circuit during start up as the generator comes up to speed. Until the generator output voltage has reached a minimum value, it is desirable to energize the exciter field with full voltage to rapidly increase the output voltage to the generator's rated value. Once a minimum output voltage is reached, it is desired to switch control of the exciter voltage to the regulator circuits for controlled energization of the exciter field and output voltage.
To solve these design problems the inventors herein have succeeded in developing a unique and novel regulator circuit which integrates each half cycle of the output voltage, compares that integrated value to a reference voltage, and switches an SCR in the exciter field voltage supply at the proper phase angle to apply a voltage to the exciter field of the proper amount to regulate the output voltage. An operational amplifier and a feedback capacitor are used to integrate the output voltage during each negative half cycle. The integrated voltage on the capacitor is discharged through a resistor and is compared with a reference voltage by a differential amplifier which compares the two voltages and triggers a pulse generator at that point in the voltage decay when the values equalize. The pulse generator generates a pulse to trigger the SCR controlled field exciter voltage supply, and also resets the voltage on the capacitor for the next half cycle.
In addition to the regulator circuit, the inventors have designed a bypass circuit which latches on the SCR in the field exciter voltage supply to permit the low residual voltage of the generator to be directly coupled to the exciter field for maximum energization during start up. After the output voltage reaches a minimum preselected value, this bypass circuitry is latched out by a pair of transistors, and the voltage regulator circuits previously described take over during normal running conditions.